JH: Yes. The CRONies study was just a cross-section. We don’t know what these people were like before they started caloric restriction. In the new study, we will recruit people who are normal to slightly overweight. We’ll ask them to eat 25 percent less than they ate before. The idea is to have people do this for two years, but that will be very difficult.

TR: What do you hope to show?

JH: At the end of two years, will these people have undergone the same biological changes as rats and mice on caloric restriction? We won’t be able to say they will live longer, but at least we’ll be able to see if the same underlying changes are taking place.

We’ll also be able to determine the maximal level of caloric restriction. For all we know, CRONies are overdoing it. Maybe you can get the same benefits with a smaller decrease in calories.

TR: One question in aging research is whether scientists can design drugs that mimic the health effects of caloric restriction (see “The Fountain of Health”). Will these studies help that goal?

JH: It will give us information on the types of biomarkers we should be looking for. If a mimetic causes the same biological changes, we can say they’re working like caloric restriction.